A polyimide resin excellent in heat resistance, electrical properties, mechanical properties and the like is being used for the surface protective film or interlayer insulating film of a semiconductor device. This polyimide resin is generally provided at present in the form of a photosensitive polyimide precursor composition and has a characteristic feature that a surface protective film, an interlayer insulating film or the like can be easily formed on a semiconductor device by subjecting the composition to coating, patterning with actinic rays, development, thermal imidization treatment and the like and the process can be greatly shortened as compared with conventional non-photosensitive polyimide precursor compositions.
However, in the development step of the photosensitive polyimide precursor composition, a large amount of an organic solvent such as N-methyl-2-pyrrolidone must be used as the developer. Meanwhile, with increased environmental concern in recent years, measures for an organic solvent-free composition are demanded. In this connection, various proposals have been recently made for a heat-resistant photosensitive resin material which is developable with an aqueous alkaline solution similarly to the photoresist.
Above all, a method where a PBO precursor composition prepared by mixing an aqueous alkaline solution-soluble hydroxypolyamide, for example, a polybenzoxazole (hereinafter sometimes referred to as “PBO”) precursor, with a photoactive component such as photosensitive diazoquinone compound is used as the positive photosensitive resin composition, is drawing attention in recent years.
This positive photosensitive resin has a development mechanism utilizing a phenomenon such that although the photosensitive diazoquinone compound in the unexposed area is insoluble in an aqueous alkaline solution, the photosensitive diazoquinone compound when exposed causes a chemical change and is converted into an indenecarboxylic acid compound which is soluble in an aqueous alkaline solution. By making use of this difference in the dissolution rate in a developer between the exposed area and the unexposed area, a relief pattern of only the unexposed area can be formed. However, in the photosensitive composition allowing the above-described photosensitive diazoquinone compound to mainly participate in the image formation, it is difficult to satisfy both high sensitivity and high resolving power, because the photosensitive diazoquinone compound solely undertakes the functions of photosensitivity and insolubility of the unexposed area.
On the other hand, as for the technique of separating the functions of photosensitivity and insolubility of the unexposed area, a large number of chemical amplification-type photosensitive compositions where an acid in a catalytic amount is generated upon exposure and the alkali-insoluble group in the composition is converted into an alkali-soluble group by a chemical reaction using the acid generated upon exposure as the catalyst in the subsequent heating process, are applied in the field of semiconductor photoresist. Also in the technical field of the present invention, a chemical amplification-type photosensitive composition is disclosed (see, for example, JP-A-2003-241377 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
However, in the chemical amplification-type photosensitive composition, the photosensitizing agent is used in a small amount for bringing out the characteristic features of the composition, as a result, the photosensitizing agent comes to be present at a low density in the film and film defects ascribable to the photosensitizing agent sometimes give rise to insufficient physical properties of the film.
Also, with recent development of the semiconductor technology, fine fabrication is required and a material ensuring high resolving power comparable to the photoresist for semiconductors and small difference (mask bias) between the mask dimension and the pattern dimension after curing is demanded. In this meaning, development of a material having a lithography performance of the semiconductor photoresist level and giving a film with satisfactory physical properties by low-temperature curing is longing for (see, for example, JP-A-2006-047377)